It is advantagous to formulate highly thickened hypochlorite bleach solutions for cleaning hard surfaces, such as drains, countertops, sinks, bathtub enclosures, lavatories, and other common household surfaces. The efficacy of liquid hypochlorite bleach cleaning compositions is greatly improved by increasing their viscosity significantly above that of a “water-thin” fluid, especially for compositions to be applied to non-horizontal surfaces in use or to be poured through standing water (as with a drain cleaner) in use. The term “highly thickened” is to be understood herein to refer to viscous compositions having viscosities of about 500 centipoise (cps) or greater at ambient temperatures of about 20-25° C.
Consumers also react favorably to highly thickened liquid products in that these fluids often connote a “concentrated” composition in the mind of the user. A common chemical approach to creating thickened hypochlorite bleach solutions is to employ surfactant-based thickening systems, which create a long range surfactant micelle structure within the composition. However, many such surfactant-based thickening systems tend to produce fluids with undesirable flow properties as the fluids become highly viscous (greater than about 500 cps). This is especially problematic at colder temperatures (below about 20° C.), as many surfactant-based thickening systems tend to increase in viscosity as the fluid's temperature decreases. Such fluids can exhibit undesirable physical and visual flow properties in use, e.g., a rubbery/elastic/lumpy or uneven flow, making the fluids difficult to dispense from the dispenser in which they are contained or visually unpleasant when dispensed. This has been observed in particular in thickened hypochlorite bleach solutions formulated with alkyl dimethyl amine oxide surfactants in combination with various co-surfactants. Examples of viscous hypochlorite bleach compositions thickened using amine oxide surfactants in combination with various co-surfactants are disclosed in U.S. Pat. Nos. 3,684,722; 4,282,109; 5,462,689; 5,624,891; and 5,703,036. Thickened hypochlorite bleach solutions may exhibit undesirable physical and visual flow properties especially when the solutions include amine oxide surfactants containing linear C14 to C18 alkyl groups. C14-C18 alkyl dimethyl amine oxide surfactants are highly desirable for thickening hypochlorite bleach solutions as they are low cost, efficient for thickening, and exhibit good chlorine bleach stability. However, the formulation of thickened bleach compositions with such amine oxide surfactants which have good pour properties at or below ambient temperature (about 1-25° C.) is difficult to achieve because such thickening systems often give rise to elastic thickened fluids with undesirable visual/physical properties (rubbery, elastic, lumpy flow) when poured from conventional containers.
U.S. Pat. No. 5,135,675 discloses the use of sulfonated polystyrene polymers in combination with clays in chlorine bleach-containing thickened automatic dishwashing compositions. The combination of thickening clays and a sulfonated styrenic polymer enhances the low shear viscosity, long-term viscosity retention and fluid uniformity in the thickened hypochlorite bleach compositions as compared to similar compositions thickened only with clays. U.S. Pat. No. 5,510,047 discloses the use of anionic styrenic copolymers as cleaning-enhancing disperants in chlorine bleach-containing detergent compositions. EP 1 001 010 B1 and EP 0 824 147 B1 disclose the use of various anionic styrenic polymers as free radical scavangers for bleach-containing compositions, for improved cleaning and storage stability. None of these patents indicate the use of the disclosed polymers to reduce the elastic character of bleach-containing solutions, nor do the patents indicate that the polymers improve low-temperature flow properties of their compositions. In addition, the noted patents set forth examples wherein the polymer additives are used in substantial quantities, i.e., greater than 0.1% and usually about 1% or more.
U.S. Pat. No. 4,839,077 employs anionic polymers produced from various combinations of charged and uncharged co-monomers in surfactant-thickened bleach compositions to synergistically increase the viscosity of the formulations in combination with the surfactant thickeners. The '077 patent discloses various copolymers formed from a combination of hydrophobic (uncharged) and hydrophilic (anionic charged) co-monomers, the most preferred being an ethylene/acrylic acid copolymer combination. While styrenic water soluble polymers are claimed in the '077 patent, no experimental evidence is provided to substantiate their efficacy. Also, the '077 patent discloses containing about 0.1% to 1.0% polymer, such that the weight ratio of surfactant thickener to polymer is from about 5:1 to 30:1 to be effective.